The present invention generally relates to a driving arrangement, and more particularly, to a bi-axial synchronous driving apparatus which may be advantageously utilized for a driving apparatus of two axes to be driven in synchronization at high accuracy in an industrial robot or the like.
Conventionally, for example, as an industrial robot for effecting various work with respect to a workpiece at high positional accuracy, there has been proposed an arrangement as shown in FIG. 3, which includes an Y-axis table 31, an X-axis table 32 which can be positioned at any desired position in an Y direction along said Y-axis table 31, and a working head portion 33 which can also be positioned at any desired position in an X direction along said X-axis table 32, with a position recognizing means 34 and working means 35 being provided on said working head portion 33 through a predetermined interval in the X direction.
In the known arrangement as described above, however, since the X-axis table 32 extends over a long distance in the X direction from the Y-axis table 31, even in the presence of a very small inclination on the X-axis table 32, when the working head portion 33 is displaced along the X-axis table 32 after positioning in the Y direction, positional deviation undesirably takes places in the Y direction.
In order to overcome the disadvantage as described above, there has been conceived another arrangement in which a set or pair of Y-axis tables are disposed in a spaced and parallel relation to each other, and opposite ends of an X-axis table are positioned in the Y direction by these Y-axis tables, while a work head portion is adapted to be positioned in the X direction along said X-axis table.
In the arrangement as referred to above, however, there is such an inconvenience that, the X-axis table can not be stably displaced unless the set of Y-axis tables are driven is synchronization with each other at very high accuracy.
Conventionally, for the driving apparatus which synchronously drives the two axes as described above, a construction as shown in FIG.4 has been generally employed. More specifically, in the arrangement in FIG. 4, position instruction signals common with detection signals of pulse generators 43 and 44 for detecting rotational positions of a set of motors 41 and 42 are applied to deviation counters 45 and 46 provided to correspond to the respective motors 41 and 42, and motor driving circuits 47 and 48 for the respective motors 41 and 42 are controlled based on deviation signals between instruction signals and detection signals outputted from deviation counters 45 and 46. Moreover, it is so arranged that the detection signals of the pulse generators 43 and 44 are inputted also to frequency/voltage (FV) converters 49 and 50, so as to apply output signals therefrom to the motor driving circuits 47 and 48 for effecting speed compensation.
However, in the bi-axial synchronous driving apparatus as explained above, the two motors 41 and 42 are controlled independently of each other with respect to the position instruction so that the deviation between the instructed position and the detected position becomes 0, and therefore, for example even in the case where a large delay in the rotational position should take place only in one motor 41 or 42 in a constant speed driving state by certain circumstances, the other motor 42 or 41 is maintained in the predetermined operating state. Accordingly, the slippage in the synchronization is not quickly eliminated, thus making it difficult to achieve synchronous driving at high accuracy.